The present invention relates to the balancing of rotors and more particularly to the balancing of rotors that are driven by a drive location on the rotor and that may, or may not, use a mechanical compensation during the balancing operation to compensate for mass(es) later attached to the rotor.
When rotors, such as crankshafts, are being fabricated, it is desirable that they be rotationally balanced so that minimal vibration will occur when the rotor is installed in its intended machine. This balancing operation commonly involves rotating the rotor to determine where there is excessive mass on the rotor which may cause vibration, and then using a drilling operation to remove mass from the appropriate region of the rotor so that the rotor is rotationally balanced.
Because some types of rotors have portions (attachment locations) that are ultimately connected to other components possessing mass, such as pistons and connecting rods that are ultimately connected to the crankpins of a crankshaft, it is necessary for some styles of rotors (for example crankshafts for a single cylinder engine, some 2, 3 and 5 cylinder engines, and for most xe2x80x9cVxe2x80x9d type engines) that the mass of these additional components be considered when the rotor is being balanced, such as by the use of a mechanical couple. The normal method for such couple compensation uses weights on opposite ends of a drive spindle and creates a couple that is a force down on one end of the drive spindle and a force up on the other end of the drive spindle. The couple mimics the influence of the mass of the other components while the rotor is being balanced. The rotor is aligned relative to the drive spindle so that these two couples are subtractive. This results in a free body system that has virtually no vibration for a properly balanced rotor. This virtual zero vibration greatly enhances the balance machine""s ability to achieve high accuracy in the process, as is well known in the art.
To properly balance a rotor, the position of the attachment locations on the rotor relative to the drive spindle must be known within a specific tolerance. For example, to properly balance a crankshaft, the position of the crankpins on the crankshaft relative to the drive spindle must be known within a specific tolerance. Previous manufacturing techniques for producing crankshafts resulted in large deviations in the positions of the individual crankpins of the crankshaft relative to one another. These positional deviations were sometimes previously required to be taken into account when balancing some crankshafts, see for example U.S. Pat. No. 4,646,570. However, in most modem production techniques for producing crankshafts, the positional accuracy of one crankpin relative to the next crankpin is within a small enough tolerance that positional deviations of the crankpins from a nominal position are no longer required to be compensated for during the balancing process. That is, the positional accuracy between the crankpins is small enough such that the deviations between these actual positions and nominal positions are usually inconsequential to the balancing of the crankshaft. Thus, if the position of one crankpin relative to the drive spindle is ascertained, the position of all the crankpins relative to the drive spindle are adequately known.
Balancing machines may drive a rotor from different locations on the rotor. The drive location or drive point on the rotor that is in contact with the driving component of the balancing machine provides a positional relationship between the drive spindle and the rotor that is used to determine the positional relationship between the drive spindle and the attachment location(s) on the rotor. For example, some balancing machines utilize a drive hole (drive location), which may be a manufacturing hole, in a flange on the end of a crankshaft to align the drive spindle with the crankshaft. (Other cranks may come to the balancing machine with a dowel pin in the drive hole. Others still use a key or keyway in the crankshaft as the drive location. Still other machines might use a manufacturing pad as the drive location to drive the crankshaft.) That is, in this example, one end of the drive spindle has a drive pin that is received in the drive hole on the end of the crankshaft to align the drive spindle relative to the crankshaft. The location where the drive pin pushes against the inside of the drive hole on the end of the crankshaft provides a positional relationship between the drive spindle and the crankshaft that is used to determine the positional relationship between the crankpins and the drive spindle. Specifically, the positional relationship between this drive location and any one of the crankpins provides a positional relationship between this drive location and all of the crankpins and is used to determine the positional relationship between the drive spindle and all of the crankpins.
Thus, the position of the drive location on a rotor relative to any one of the attachment locations must be known to within a specified tolerance to properly balance the rotor. The position of the drive location relative to the attachment locations, however, may deviate between rotors and this deviation may need to be compensated for during the balancing operation. For example, in a crankshaft the position of the drive location relative to the crankpins may deviate between crankshafts, due to any combination of drive hole location, size and shape errors, to an extent that would result in improper balancing of the crankshaft if the deviation is not compensated for. Accordingly, it is advantageous to account for deviations in the actual position of the drive location relative to a nominal position of the drive location when balancing a rotor. It is also advantageous to account for such deviations during the actual balancing process as the rotor is spinning to reduce cycle time and associated manufacturing costs.
The present invention provides a drive location compensation system that compensates for a deviation between the actual position of the drive location relative to a nominal position of the drive location when balancing a rotor, such as a crankshaft. The system provides such compensation during the balancing operation of the rotor so that such compensation has a minimal effect on the cycle time of balancing a rotor.
A system for balancing a rotor having a drive location and at least one attachment location to which component(s) possessing mass are later attached, according to the principles of the present invention is disclosed. The system includes a balancing machine operable to balance the rotor. The balancing machine includes a spindle operable to couple to the drive location on the rotor being balanced. The spindle rotates the rotor during the balancing operation. There is also an attachment location sensor operable to sense a position of the attachment location on the rotor being balanced. A deviation between a nominal position of the drive location and an actual position of the drive location on the rotor relative to the attachment location on the rotor is compensated for during the balancing of the rotor.
A method of balancing a rotor having a drive location and at least one attachment location to which component(s) possessing mass are later attached is also disclosed. The method includes: (1) determining a deviation in a relationship between the drive location on the rotor and the attachment location on the rotor; and (2) compensating for the deviation when balancing the rotor.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.